High-frequency heating apparatus



J. A. REDMOND HIGH-FREQUENCY HEATING APPARATUS Nov. 22, 1955 2Sheets-Sheet 1 Filed Aug. 12, 1950 Network Generator L INVENTOR John A.Redmond.

ATTORNEY Nov. 22, 1955 J. A. REDMOND 2,724,763

HIGH-FREQUENCY HEATING APPARATUS Filed Aug. 12, 1950 2 Sheets-Sheet 2Fig.3.

O O O O O O O O O O O O O O O D WITNESSES:

INVENTOR John A. Redmond.

BY92Z ATTORN EY United States p fl 2,724,163 HIGH-FREQUENCY HEATINGAPPARATUS John A'. -Redmond, Baltimore, Md;,-- assigno'r' {to'Westinghouse Electric Corporation, East llittsburghyPaacorporationtofiPennsylvania Application August 12,1950, Serial No.179,078

'4 .Claims. KC]. 219-10179) .My invention relates broadlytohigh-frequency heating; .but, more particularly, my invention is"directed .to .improvements in apparatus for the'h'igh-frequenc'yheatingof a tubular object, by tubular object meaning an object having.a central opening capable of receiving .an electrical conductor.

.A purpose of my invention-istto provide.ahighfrequency heatingapparatus capable of heating a tubular metallic obect by heatingcurrents magnetically induced .therein in a mannerthat causes thecurrents to flowjlengthwisqor axially of the opening in the object,instead-of in apath around the axis as taught by theprior art.

A further object of my invention is to provide .aninduction heatingapparatus of a type described, capable 10f heating a tubular object,such as a small hollow shaft or bushing; the apparatusbeing such asto'be capable of simultaneously heating the inner and outer.surfacesTo'f the object.

In accordance with the teachings of my invention, I provide a pair ofnested inner and outer heating conductors which are connectedelectrically .sothat current flows lengthwise or axially along both ofthem. Thecon- .ductors are spaced, and thefinnerconductorisplaced'ins'ide of the opening of the tubular object totbefheated,preferably out of contact with the conductors. When current flowsthrough the conductors, the object .is heated. In the .case of a ferrousobject, theapparatus can be arrange'difor'hardening a surface of theferrous object by perforatinga wall of one or both of 'the conductorsand passinga quenchingliquid through the perforations or openings at asuitable time.

'Objects,'features and innovations of my 'inve ntion,.in addition to theforegoing, will be discernible from thexfo'llowingdescriptionofillustrative apparatus embodying the invention. The description is ,tobetaken in conjunction with the accompanying simplified drawings, inwhichudetails such as work-handling holders, and .so forth, .areomittedin the interest of clarity and brevity. In the drawings:

Figure l is asomewha't diagrammatic view of. apparatus embodying myinvention;

Fig. 2 is a sectional viewsubstantia'lly on the 11inen n of Fig. '1;

Fig. '3 is a vertical sectional view of a preferred embodiment of myinvention, the section-plane being indicated by the broken line 'IIIIIIin Fig. 4;

Fig. 4 is a plan view of the apparatus ofFig". 3;

Fig. 5 is a sectional view substantiallyon the line'V-V .ofFig. 3; and gFig. 6 is a sectional'view substantially onthliriVI-VI of Fig. 4.

Figs. land 2 show a simplified induction heating apparatus, illustrativeof 'theibroad principle of "my invention, that can be used for heatingbushings." The, apparatus comprises an induction heaterwhich isindicated in its en- "tirety 'byth'e reference numeral'Z. Theinductidnheater2 comprises a straight inner heating conductor '4 and astraightouter heating'conductor 6; The conductors are'ciroi-'18,)'.are"secured.Such points on each heating conductorare axially spaced,one pair of spaced points (-as cularin cross section andkaremade ofahighly conducting metal such as copper. The outerconductor 6 is hollowso thatthe'inner conductor 4 'canbe nested therein,;prefe'rably paralleland concentric therewith. The'bottomends of the heating-conductors 4 and6.are intimately electrically connected together by a conductor-meanscomprising a direct electrical connection-conductor shown as anannularplate '8 whichfis also made from ahighlyconductive metal.

I Theheating conductors 4 and .6 are radially spaced,i. e., they areseparated in a direction perpendicular to their common axis, so as toprovide awor'k-receiving space 10 'therebetween. This [space 10 isgenerally annular in cross section and is bounded'by the outer or facingsurface of the innerheating conductor 4, "the inner or facing surface ofthe outer heating conductor 6, and the inner or facing surface of theconnection-plate 8.

' Atubu'lar object 11in the formof a cylindrical tube, is supported 'inthe work-receiving space 1'0 in any suitable manner for 'heat treatment..A work-supporting means is shown as comprising aplurality of spacedpiers 14, carried "by the connection-plate 8. Eachpier has a seat ornotch for receiving .an end of the tubular object 12. The piers are madeof a material that 'willstand a high temperature, and molybdenumhas beenfound satis'factoryfor this purpose.

- 'A't'the ends 'of the'heating conductors 4 and 6 which are opposite tothose associated with the connection-plate 8, a pair of relativelyinsulated power-supply conductor-connections16.and' 18 are provided; theconnection 16being intimately securedlo-it'he inner heating conductor 4and "the connection 18 'being similarly secured to the outer.heatin'g'cdnductor 6. The 'relat'ive'lyin sulated power supply*conn'ect'ions16 and 18 are supplied with high-frequency energy,generatedin a'high frequency generator 20 that "feedsithe generatedcurrent to them, either directly or .through asuitablecircuit' 22 thatmay include a balancing networlcor transformer, or other electricalcircuit-improviin'g' element, as 'isknown 'to'the 'art.

*It is necessary to provide away of placing an object to .beheat-treated into the work-receiving space '10 and "can beused.

For an understanding of the. operation of the induction 'heater '2, itmaybe assumedlthat the high-frequency generator-20 is .energized'and isfeeding high-frequency elec- 'trical"power'to the conductor-connections16 and 18. It canbe' assumedzthat, atsome instant, thecurrent is flowingfromth'e connection 16, downwardly along the outer surface of'the innerconductor t, :radially outwardon the inner surface of theconnectiomplate 8, and upwardly "along the :inner surface of the outerconductor 6, to the ofaxially spaced'points, one ateach of .its ends, towhich 'circuivconnec'ti'ons (that is.plate 8 and a connection '16:16'and 18)"co'nduc'torlying on one axial side of the worktreating space10 and the other pair'of spaced points (as '4-"8-an'd'6 8) lying on'the'opposite side.

The alternating current, flowing .in the conductors 4 and 6; inducesrheating currents in the metal tubular object "12 which is carriedonihe'piers'14, preferably concentric with-theheatingconductors. Theinduced currents will fiow in e'ach "curved side of the tubular object,and in a direction opposite to the direction in which the current flowsinthe' surfaces 'of the facing heating conductors.

Accordingly, at t'h'eflassumed "instant, current will flow upwardly"along the elements "of the inner "surface of the tubular-"object "anddownwardly along the outer surface pleted in a radial direction at theends of the tubular objects. The induced current heats the surfaces ofthe object in a manner understood in the art.

It is understood, of course, that the current flows in a thinsurface-film having a thickness or depth which depends, among otherthings, upon the frequency of the power delivered by the high-frequencygenerator.

If it is found necessary to cool the'heating nested conductors 4 and 6,an outer cooling-coil 24 may be helically wrapped around the outsidesurface of the outer conductor 6, in good thermal contact therewith, andan inner cooling-coil 26 may be disposed in contact with the insidesurface of the inner conductor 4, which can be made hollow for thispurpose, as shown in Figs. 1 and 2. The outer coil 24 has a water-inlet28 and a water-outlet 30; and the inner coil 26 has a water-inlet 32 anda water-outlet 34, extending downwardly through the open bottom of theheating conductor 4.

Figures 3-6 show a more practicable structural form of my inductionheater, indicated in its entirety by the reference numeral 40. Theinduction heater cornprises an inner copper heating conductor 42 and anouter copper heating conductor 44. In the preferred embodimentillustrated in Fig. 3, the outside diameter of the inner conductor 42 isone inch, and the inside diameter of the outer conductor 44 is threeinches. The lower end of the inner conductor 42 has an integraloutwardly extending flange or connection-plate 46, to which the lowerend of the outer heating conductor 44 is firmly joined, for intimateelectric contact. The conductors 42 and 44 are radially spaced toprovide an annular work-receiving space 48 (Fig. 3) similar to the space10 of Fig. l.

The inner conductor 42 is hollow, having an open lower end and a closedupper end 50 that terminates in an upwardly extending threaded portion52 which projects above the upper end of the outer heating conductor 44.The hollow part of the inner conductor 42 forms a channelmeans 54, whichis defined by the cylindrical wall 56 of the conductor 42, and which isperforated to provide ou'tlet quench-openings for a quenching-liquidwhich is fed into the channel 54 in any suitable manner. Thus, saidchannel 54 may be supplied with a quenching-liquid through a pipe 58.The inner heating conductor 42 may be cooled, if necessary, by a helicalcooling coil 60, which contacts the inside of the wall 56 and which isprovided with water inlet and outlet-pipes 62 and 64, respectively,which extend downwardly through the lower end of the inner heatingconductor 42.

The outer heating conductor 44 is ,also constructed so as to permit theoutside of the work-piece to be quenched. To this end, the outer heatingconductor 4.4.is hollow to provide an annular channel-means 68 therein.Specifically the outer conductor 44 comprises a solid or imperforateouter tubular wall 70, and a perforated inner tubular wall '72.Quenching liquid is supplied to the annular channel 68 of the outerheating conductor 44 by means of one or more liquid-supply pipes 76. Forkeeping the inner wall '72 of the outer heating conductor 44 cool, a

cooling coil 74 is helically wound around it in intimate thermal contacttherewith. This cooling coil is provided with water inlet and outletpipes which liquid-tightly pass through the outer wall of the outerheating conductor.

The work to be heat-treated is represented, in Figs. 3-5, as a ferrousbushing 78. 80, which in turn are replaceably and snugly carried ingrooves of a turntable 82 which is adapted to rotate around the lowerend of the inner heating conductor For rotating this turntable, a belt84 is provided which passes through tubes 86 passing through the outerheating conductor 44.

The upper end of the outer heating conductor 44 has an integral flangeor copper plate 90,-that closes the upper end of the annular channel 68in said conductor 44.

It is carried on notched piers diameter to the inner diameter of thewall 72. Secured tube-oscillator generators. as shown in Fig. 3, I havesuccessfully hardened both to the underside of this top-plate 90 is aconductorconnection 92. Resting on the top-plate 90 is a layer ofinsulation 94 which separates said plate from a secondconductor-connection 96. The connections 92 and 96 are equivalent to theconnections 18 and 16 of Fig. 1. As shown in Fig. 4, the insulation 94,the lower connectionplate 92 and the upper connection-plate 96 haveU-shaped cutout portions 98 that extend beyond a side of the outerheating conductor 44.

For electrically connecting the connection 96 to the inner heatingconductor 42, a narrow copper securingbar 100 is provided, having threespaced holes, the central one of which receives the extending threadedportion 52 of the inner conductor 42, and the end ones of which receivethreaded bolts 102 and 104 that extend upwardly from the connection 96.Nuts 106 clamp the securing bar 100 in intimate contact with theconnection 96 and with a flange 108 at the top of the inner heatingconductor 42. Accordingly, whenever work is to be inserted into, orremoved from, the work-receiving space 48, the securing bar 100 is firstremoved.

Assuming that work to be heated is in the space 48, the securing bar 100is tightly bolted down, and the relatively insulated connections 92 and96 are energized from any suitable source of high-frequency energy. Theturntable 82 is rotated for rotating the Work carried on the piers 80.After the desired heating interval, quenchingliquid is supplied to thechannel-spaces 54 and 68 for hardening the inner and outer surfaces ofthe bushing. Quenching liquid may flow out of the work-receiving space48, through a plurality of spaced openings 109 in the bottomconnection-plate 46. It is also to be observed that the connection-bar100 is of less width than the inner diameter of the outer heatingconductor 44. Consequently, quenching-liquid can also flow upwardlythrough the resulting opening, including the cutout portions 98.

An induction heater in accordance with my invention may be used withpractically any of the more common frequencies now used for inductionheating. I have used electric power derived from rotating alternatorsand from In a particular setup, such surfac'esof a six-inch bushing byusing current at a frequency of about ten thousand cycles per second andflowing at eight thousand amperes. I have also used similar equipmentfor hardening with currents at considerably higher frequencies. The wavelengths are considerably longer than the work-piece 12 or 78, so thatthere are no significant standing-wave effects in the heating apparatus,to produce non-uniform heating patterns in the workp ece.

In general, the object to be heated should have its axial- 'ly extendingcurved surfaces radially spaced about equally from the heatingconductors. Non-equal radial spacing causes non-uniformcurrent-distribution in Fig. 2. In

'Fig. 3, rotating the workpiece 78 produces even heating;

even though the radial spacing may be non-equal. For this reason, it isdesirable to rotate the piece.

While I have described my invention in connection with an embodimentwhich is at present preferred, it is obvious that this embodiment issubject to considerable changes and modifications, and that theprinciples of my invention have considerably larger application, beyondthat described in connection with the preferred embodiment.

I claim as my invention: 4 1. High-frequency inductive-heatingapparatus, including a supporting-means for holding a hollow cylindricalconducting object having interior and exterior surfaces to be heated,and high-frequency inducing-current means comprising an inner tubularinductor member and an outer 'tubular inductor member respectivelypositioned adjacent the interior and exterior surfaces of said object,for subjecting said surfaces to high-frequency current-inducing fieldssuch as to induce high-frequency surface-skin cur rents which flowaxially and in opposite directions along the respective interior andexterior surfaces of said object and radially at the ends of saidobject.

2. High-frequency inductive-heating apparatus, including asupporting-means for holding a hollow cylindrical conducting object tobe heated, said object having substantially parallel interior andexterior surfaces, motor means for rotating said supporting-means aboutan axis which is approximately coincident with the axis of said object,and high-frequency inducing-current means comprising inner and outertubular inductor members, said latter members being positioned adjacentrespectively the interior and exterior surfaces of said object forsubecting said surfaces to high-frequency current inducing fields suchas to induce high-frequency surface-skin currents which flow axially andin opposite directions along the interior and exterior surfaces of saidobject and radially at the ends of said object.

3. High-frequency heating apparatus of a type described, comprising, incombination, a plurality of nested heating conductors including an innertubular induction heating conductor and an outer tubular inductionheating conductor, said conductors extending in the same generallengthwise direction and being radially spaced to provide awork-treating space therebetween, work-supporting means for holding anaxially extending workpiece in said space, said workpiece beingpositioned substantially parallel relative to said conductors, andcircuit-means for supplying high-frequency current to said conductors,said circuit-means including circuit-connections between a pair ofspaced connection-points on each of said conductors, said pairs ofpoints being on opposite sides of the work-treating space, saidcircuit-connections including a direct cross-connection between a firstof said points on said inner conductor and a first of said points onsaid outer conductor, said first points lying at the same end of saidwork-treating space.

4. An induction heater of a type described, comprising, in combination,a pair of nested substantially parallel tubular induction heatingconductors, said conductors being radially spaced to form a space forreceiving work to be heated, conductor-means directly connecting anend-portion of the inner of said conductors to an endportion of theouter of said conductors, said conductorrneans being at an end of saidspace, means for supporting a metallic object in said space, with theinner conduc tor passing through said object, means for providing accessto said space for loading and unloading said metallic object to and fromsaid space, said means being at the other end of said space, andpower-supply means associated with said conductors for causing highfrequency currents to flow axially in said conductors.

References Cited in the file of this patent UNITED STATES PATENTS1,566,500 Northrup Dec. 22, 1925 1,987,458 Adams Jan. 8, 1935 2,145,864Denneen et al Feb. 7, 1939 2,181,921 Schlup Dec. 5, 1939 2,294,413Marshall Sept. 1, 1942 2,359,285 Bennett Oct. 3, 1944 2,364,623 Denneenet al Dec. 12, 1944 2,404,987 Rudd July 30, 1946 2,449,325 Rudd et al.Sept. 14, 1948 2,483,623 Clayton Oct. 4, 1949 2,517,098 Dreyfus Aug. 1,1950 2,556,236 Strickland, Jr. June 12, 1951

